code: def test_precision_empty_none():
      prec = _test_prec([], [1, 3])
      assert prec is None
  
file_path: lkpy/tests/test_topn_precision.py
imports: import numpy
  import pandas
  from pytest import approx
  from lenskit.topn import precision
  from lenskit.util.test import demo_recs
  from lenskit import topn
label_desc: Use image node_id 2 for calling a global function with example usage: test_precision_empty_none() without return types